The rules are not "for" something in France. They just appear out of committees and political compromises and are often half-assed implementations of nonsensical middle-ground between two coherent positions. Some may occasionally align with public interest.

One of the things you learn living in France is a sense of the rules that make no sense and that everybody is probably disregarding, and the ones that are actually useful and probably enforced.

Always smile to a clerk. They will tell you which mandatory paper is not mandatory and which rule you can break. They will also tell you which rule the state is incapable of following and how to get around it.

To selectively enforce against people you arbitrarily do not like.

To provide some means for censuring those people who flagrantly disregard the unwritten rules (I know that, formally, that looks nonsensical, but in practice it is not.)

With traffic, agreement often matters more than the specific rules.

The rules are supposed to be a universal agreement. Otherwise it makes it very dangerous to drive in a different city even though the laws are the same.

This is why lots of people die every year in traffic accidents.

They are.

Try driving in Asia and get back to me.

(Disclaimer: I'm hard line traffic law follower.)